<!-- 
    quadraticCurveTo(cp1x, cp1y, x, y)
        绘制二次贝塞尔曲线，
        cp1x,cp1y为一个控制点，
        x,y为结束点。
 -->
<html>

<head>
    <title>Canvas tutorial</title>
    <script type="text/javascript">
        function draw() {
            var canvas = document.getElementById('canvas');
            if (canvas.getContext) {
                var ctx = canvas.getContext('2d');

                // 二次贝塞尔曲线
                ctx.beginPath();
                ctx.moveTo(75, 25);
                ctx.quadraticCurveTo(25, 25, 25, 62.5);
                ctx.quadraticCurveTo(25, 100, 50, 100);
                ctx.quadraticCurveTo(50, 120, 30, 125);
                ctx.quadraticCurveTo(60, 120, 65, 100);
                ctx.quadraticCurveTo(125, 100, 125, 62.5);
                ctx.quadraticCurveTo(125, 25, 75, 25);
                ctx.stroke();
            }
        }
    </script>
    <style type="text/css">
        canvas {
            border: 1px solid black;
        }
    </style>
</head>

<body onload="draw();">
    <canvas id="canvas" width="150" height="150"></canvas>
</body>

</html>